Some people experience greater levels of myopic refractive error (short-sightedness) at night compared to daytime vision. This disorder, known clinically as night myopia, was first described around the end of the 18th century by the presbyopic Royal Astronomer Reverend Nevil Maskelyne concerning his observations of distant stars without refractive correction as well as with daytime negative correction and slightly more negative lenses. A similar problem was noted almost a hundred years later in 1883 by Lord Rayleigh describing difficulties in identifying small objects under bad light conditions. Yet, more than two centuries later night myopia remains a poorly understood and enigmatic subject of study. A number of explanations for night myopia have been hypothesized Yet, in spite of these hypotheses, no definitive explanation for the aetiology of night myopia has been provided.
Reliable techniques for correction of night myopia could benefit many patients that experience reduced vision at night. Night myopia is a common patient complaint heard by practicing optometrists and is a recognized hindrance to safe nighttime driving and other nighttime activities. Heretofore there has been no reliable method or technique for determining the necessary adjustment to daytime prescriptions to correct for night myopia. Past attempts at providing such corrective prescriptions have been based on methods or explanations for night myopia such as the optics of the eye changing due to a larger pupil size, the presence of higher-order aberrations, an involuntary accommodative response produced under low lighting conditions, accommodation, or chromatic shift in scotopic light conditions.
Some past attempts to improve night vision, such as the approaches described in U.S. Pat. Nos. 4,943,151, 4,997,269 and 5,223,866, rely upon measuring dark focus acommodation of an eye under low ambient light levels or a refractive change between night and day lighting conditions with optometers in the hope of providing a better prescription. Other past attempts, such as the approach described in publication no. US 2003/0020988 A1, have proposed the prescription of lenses having some additional negative lens power, for example, between −0.12 to −1.00 diopters, based upon a trial and error approach. Further past attempts, such as that described in U.S. Pat. No. 7,364,299, rely upon objective, instrument-based measures of visual function such as measurements of mesopic vision and abberation.
The foregoing and other conventional attempts to improve night myopia have been hindered in part by incomplete and incorrect explanations for the causes of or factors contributing to this affliction. One explanation posits that uncorrected myopia or deliberate under-correction of myopia produced by maximum-plus refractions is less noticeable during the day when high levels of ambient luminance reduce the size of the eye's pupil, thereby reducing the amount of blur on the retina. Another explanation assumes that most eyes have positive spherical aberration (SA) when accommodation is relaxed which means the optical power of the eye is greater at the pupil margin than at the pupil center implying that the visual effects of spherical aberration will be most noticeable under dim illumination conditions. A further explanation is that optical image quality in any optical system exhibiting SA can be improved by a judicious change of focus. Yet another mechanism posited to contribute to night myopia arises for very dim (scotopic) illumination levels for which the fovea is blind. These and other conventional theories and explanations have proven to be at best incomplete and sometimes incorrect.
Existing attempts to improve night vision suffer from a number of limitations and drawbacks. They fail to account for the preference of the observer or visual performance in a vision test. They rely upon trial and error and are based on theory that is at best incomplete if not outright mistaken. They do not consider or account for the type or nature of visual stimulus encountered by a patient. They are based upon inadequate and incompletely defined metrics and definitions of improved vision and incomplete or incorrect explanations for the causes and factors contributing to night mypoia. These and other shortcomings have left the state of the art for improving night vision unsatisfactory to many patients and clinicians. There remains a longfelt need for the unique and inventive methods, systems, and apparatuses disclosed herein.